Re: Add 64-bit XIDs into PostgreSQL 15

On Mon, 9 Feb 2026 at 18:03, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:

>
> The point is that we still do not want to use FullTransactionID
> everywhere. Only in some places related to visibility checks that need
> to deal with XIDs stored on sidk, like heapam_visibility.c and clog.c,
> and it will probably spill over to some other places. But things like
> the proc array can continue to use 32-bit XIDs.
>
> We will still have the limitation that you cannot have two transactions
> *running* that are more than 2 billion XIDs apart. I think that's fine,
> and we should not try to lift that limitation as part of this patch.
>
> The aim of this patch is to make Postgres support 64-bit XIDs.
This is why the TransactionID type size increases from 4 to 8 bytes.
It also has an effect on the proc array, allowing two transactions that
that are more than 2 billion XIDs apart to run at the same time.

You couldn't store tuples that were more than 2 billion XIDs apart
on a single heap page. That is correct. However, this annoying
limitation comes only from the page format. Moreover, it looks like
as long as we have a page format with a base, we will not be able
to bypass this limitation. Yet, running transactions far apart is
totally accepted.

--
Best regards,
Maxim Orlov.